A power usage calculation system measures a power usage per unit time and calculates a total amount of the power usage by aggregating the measured data. A third party or the like can thus refer to the measured power usage and guess the power usage of an individual or a group (a measurement destination), thereby possibly leading to the invasion of privacy. It is therefore required for the power usage calculation system to protect the privacy of the measurement destination with regards to the power usage being aggregated. Concerning such requirement, there has been proposed a method in the related art where the measured power usage is encrypted so that information on the power usage is processed while concealed.
However, the method in the related art cannot detect falsification of data.